CA1036665A

CA1036665A - Hermetically sealed storage battery with grid-supported electrodes

Info

Publication number: CA1036665A
Application number: CA204,886A
Authority: CA
Inventors: Samuel Ruben
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-07-16
Filing date: 1974-07-16
Publication date: 1978-08-15
Also published as: DE2434193B2; JPS5330893B2; DE2434193C3; DE2434193A1; JPS5049632A

Abstract

Hermetically Sealed Storage Battery Abstract The invention comprises a storage battery having a positive electrode of lead peroxide supported by a grid of titanium having a polarization inhibiting layer between the titanium and the lead peroxide a negative electrode of lead supported by a grid of stainless steel and an electrolyte of sulfuric acid, preferably gelled, containing a small amount of titanyl sulfate. The battery is hermetically sealed.

Description

lQ36665 This invention relates to a storage battery utilizing the reversible charging characteristics of a lead peroxide positive electrode and a porous lead negative electrode in contact with an electrolyte of sulfuric acid. The lead peroxide reactant is supported on a thin grid of titanium, preferably expanded and stretched and the porous lead reactant is supported on a thin grid - of stainless steel, likewise preferably expanded and stretched.
The stainless steel is of the chromium-nickel-iron type, such as ~ -#304, having a nominal composition of 18% chromium, 8% nickel,

2% manganese and the balance iron. To avoid polarizing effects, ~ both positive and negative grids are preliminarily plated with a - thin layer of nickel and then lead plated. The electrolyte is ;
gelled by the addition of sub-micron silica.
I have found that chemical attack on shelf by the sul-furic acid electrolyte on both the titanium and the stainless steel grids may be reduced to a negligible amount by adding about 1% of titanyl sulfate (TiOSO4) to the sulfuric acid. The titanyl sulfate -~acts as inhibitor for both the stainless steel and the titanium, making both of them passive to the sulfuric acid electrolyte when on shelf. The titanyl sulfate may be the commercial basic sulfate dissolved into the sulfuric acid by heating the solution to a temperature of about 90C.
While stainless steel having a heavy lead plate is useful to a limited extent as a supporting grid for the positive electrode, I have found that after a number of cycles, it is anodically attacked with resultant cell failure.

` ~' ' .
'.

..
,. , .. ~ ;. . .

The use of titanium as the supporting grid for lead - peroxide requires an integral non-polarizing layer between the grid and the oxide that will prevent a potential gradient from being established between the titanium and the electrolyte. While I have previously used a gold film to prevent polarization, I have ` now found that I may dispense with the use of gold, by first plat-ing the titanium with a thin adherent coating of nickel, followed by an integral lead deposit of low porosity derived from a fluoborate solution.
` lO I have discovered that by dissolving a small amount of titanyl sulfate in sulfuric acid, stainless steel, particularly - the types composed essentially of iron, chromium, and nickel, such as the #300 series, may be exposed to or immersed in the solution without being attacked. The addition of the titanyl sulfate appears to completely passivate the stainless steel and thus per-- mits the use of a thin light weight reactant support affording excellent current distribution with minimal ionic polarization.
In conventional lead acid storage batteries as present-ly used, a large proportion of the weight results from the use of the heavy massive lead electrodes and grids. The use of titanium as the positive electrode base and stainless steel as the negative electrode base, permits a very substantial ~eduction in weight (density of Ti=4.3 grams/cm3 and density of #304 stainless steel approximately 4.9 grams/cm3 at 20C as compared to Pb at 11.342 grams/cm at 20C). Expansion and stretching of the comparatively thin titanium and stainless steel grid materials to a degree not practically feasible with lead, provide maximum areas of exposure of the retained oxide to the electrolyte with improved mass utilization. The amount of the active mass efficiency cited in the literature for lead acid batteries is between 35% and 50%.
This is accounted for by the restrictions imposed on the lead grid structure. In my battery, as described herein, the path length .. .. . - . . .. ~ ,..... . .

~036665 between the PbO2 and the electronic conductor is small, which allows a mass efficiency of 83% to 90% at 12 hour rate. Titanium and stainless steel being .: . :
.. . .

. . .

~,-.
. ~

~:
. ' ' - 2a -.' . .

.
. ~

;~'' 1036665 O~ high tensile strength, large size electrodes may be utilized, beyond the practical limits of lead. The use of these grids allows uniform distribution of current and contact with the reactants during the reversible reaction of PbO2 + Pb +/H2So4~ 'tPbso4 + ~2 An important aspect of this invention is that the nature of the battery elements permits a hermetically sealed con-struction. The active cell structure is sealed in an epoxy resin, producing a truly maintenance-free structure. The assembly of the 10 cell constituents, in combination with the gel electrolyte, allows internal reconversion of any extraneous gases in the restricted and sealed-off area of the electrodes.
To obtain a strong, solid epoxy seal, it is necessary, before encapsulation to completely and tightly wrap the assembled cell in resin-impermeable acid resistant plastic film. This plas-tic film seal serves a dual purpose - - - it prevents the egress of any immobilized acid gel into the resin while the resin is in a liquid state (contact of the resin with the electrolyte would -prevent hardening of the resin); it prevents ingress of the resin into the gel electrolyte, reaction with, would affect the proper electrochemical operation of the cell.
The use of the expanded titanium and stainless steel grids, permits the construction of batteries in a variety of shapes and makes possib~e the utilization of plates much larger than feasible with conventional lead structures. Two types of cells of this invention are illustrated in the accompanying drawings in which:-Fig. 1 illustrates a cell according to one embodiment of the present invention of a rectangular structure;
Fig. 2 is a horizontal section through the cell of Fig. 1 along the line 2-2;
::
~ - 3 -.
., ~ .

--- ~.036665 Fig. 3 depicts in some detail the structure of terminal (2);
Fig. 4 illustrates a polyethylene frame used in the cell of Figs. 1 and 2;
Fig. 5 illustrates a cell according to another embodi-ment of the present invention of a cylindrical structure; and Fig. 6 is a section along the line 6-6 in the cell of Fig. 5.
The following description of the materials, processing and assembly of the parts in these two embodiments will be useful in describing the invention in some detail. The terms "positive"
and "negative" electrodes as used herein, refer to the output polarities.
` Referring to Figs. 1 and 2, the positive electrodes (1) having an integral tab section and external lead (2) utilize a grid of 0.010" thick pure ~ ~

` . ~ ,-~' `

~,:
.' ' . ' '.
'' - ' ~,: -- 3a -' -' .:. :-.. -. -titanium, expanded and stretched to a diamond-shaped pattern of 0.060"
overall thickness. A-fter degreasing, chemical cleaning -for 70 seconds in an arnrnonium fluoride - ammonium bifluoride solution, and water rinsing, a very thin nickel plating from a NiS04/NiC12/boric acid solution is ap-plied to the grid which is t-hen rinsed and dried. For a grid 3 2/16" x 4 5/16" having an integral tab section 1 1/8" x 2", the plating may be applied in 1 minute at a current of 5 amperes with a deposition of .091 grams. The nickel plated grid of the above dimensions is then lead plated at a current of 4 amperes for 1 hour in a lead fluoborate solution so that approximately 15.4 grams of lead is deposited, intimately bonded to the nickel surface. The lead plated grid is then coated with approximately 70 grams (weight a-fter drying) of paste made by grinding 60.0 grams of red lead, 8.4 cc6% by volume H3P04, (7.1 cc 85% il3P04/92.9 cc. H20) and 2.8 cc of a solution consisting of 5 parts by volume 1.400 s.g. I-l2S04 and 1 part by volume 1.311 s.g. titanyl sulfated }l2S04. The coated plates are air dried for 24 hours, then immersed for 10 minutes in a solution consisting of 5 parts by volume 1.400 s.g. H2SOa and 1 part by volume 1.311 s.g.
titanyl sulfated H2S04. Following dipping, the electrode is air dried for 48 hours.
The negative electrode (6) of the same dimensions as the positive grid, having an integral tab section and external lead (7) utilizes stain-less steel #304 fully annealed, 0.008" thick, expanded and 9tretched to a diamond-shaped pattern of 0.045" overall thickness~ After degreasing, cleaning in HCl solution and cold water rinsing, a flash nickel plating ( 5 amps for 30 seconds in NiC12/llCl solution) is applied to the grid, which is then rinsed and dried the weight of the deposited nicliel being .0152 grams. Thereafter a lead plating is applied over the nicl;el in the same manner as described for the positive grid. The lead plated grid is then coated with the same materials and in the same rnanner as the positive grid, except that the thinner negative grid holds less mix - approximately 60 grams.

~036665 The initial nickel plate appears to be essential for both the titanium and stainless steel in maintaining a bonded coating.
While nickel is the preferred plate, cobalt may also be used. Lead plating over the thin nickel plate has proved to be a practical meCb-od for maintaining satisfactory operation over many cycles.
The coated grids as described above~ are than electro-for~ed in 1.070 s.g. H2S04+1.0% by volume 85% of N3P04 to their -respective reactants, PB02 on the~positive electrode and porous Pb on~ the negatibe electrode.
Thin sheets (3) of unwovern glass cloth coated with gel electrolyte (5) are placed in contact with the positive eldctrodes and 0.060" thick polyethylene frame (4), illustrated in Fig. 4. The frame has a 1/8" wide border and a 1/8" centerstrip. The gelled electrolyte is a non-separating self-supporting gel madeby mixing sub-micron sise silica with sulfuric acid containing a saturating amount of titanyl sulfate. It is confined within the open areas of the frame, the walls of which prevent squeezing out or loss of electro-lyte when the assembly is compressed and encapsulated. The electrolyte Permeatesthe glass spacers and is in initimate adhering contact with the negative electrode. The gelled acid, confined by the polyethylene frame spacers~ provides a relatively immobile electrolyte which reduces local chemical action by eliminating free circulation of the electrolyte with dissolved by-products. As will be seen~ the cell assembly comprises two positive electrodes and three negative electrodes separated by the gel filled unwoven glass cloth spacers and electrolyte filled frames. Sheets of untreated glass cloth (8), adjacent to the two . : .:. '. ' -~036665 outer negative electrodes, serve as compressible and absorbent end members. The assembly is tightly wrapped and enclosed in vinylidene chloride (supplied under the trademark Saran) film, (9) the wrapping being taped with "Scotch" (a trademark) brand tape - to close any open areas and complete the sealing of the cell.
Plastic container (11) is filled up to 1/4" from the top with ~-epoxy resin (10), the resin being poured at a temperature of 60C.
The cell unit is slowly dipped into the container so that the resin fills all spaces. After the encapsulating resin has hardened, the remaining space at the top of the container is filled with epoxy resin to which 10% by weight of finely divided silica has been added to form a hard white top seal.
During epoxy encapsulation and due to the exothermic reaction of the epoxy resin as it hardens, the elevated temperature of the immersed unit will cause displacement and discharge of air -and occluded gases until the resin hardens and seals. The con-tainer must be of adequate thickness and strength not to distort ' under the conditions of expansion and contraction accompanying -these temperature changes, as well as during the period of initial gas generation during the first cycle of charge. In operation, no progressive change in battery dimension occurs.
A container made from stainless steel, tin plate or other suitable metal may be used instead of a plastic case to house the cell and encapsulating medium. Metal cans are prepared by first degreasing internally and then applying an internal -~ coating of epoxy so that all surfaces are completely covered. By ; permitting the excess epoxy to drain to the bottom of the can as curing takes place, a good bottom seal is assured.
Figure 3 depicts in some detail the structure of terminal (2). The expanded titanium grid has an integral portion serving as the external lead.
The use of a metal other than titanium as the negative .

electrode is basically necessary. Titanium as a negative electrode reacts with hydrogen and dissolves, losing its mechanical strength and solid metal structure to some extent in the initial formation process, and even more so after a few cycles. This occurs in time regardless of whether the titanium is initially lead plated.
Previously I have utilized lead plated expanded copper grids as the negative electrodes, and these were an improvement over titanium; however, on extended storage, some copper was dissolved into the electrolyte and redeposited as an oxide on the lead peroxide positive electrode with consequent reduction of cell voltage and storageability. In endeavoring to use stainless steel as a negative grid material, I found attack of the stainless steel, with nickel, iron, and chrome sulfate appearing in the gel electrolyte. I discovered that adding titanyl sulfate (TiO SO4) to the 1,3000 S.G. sulfuric acid electrolyte (raising it to 1.311 S.G.~ made the stainless steel of the #304 type so passive that only negligible traces could be determined in the electrolyte after - a long period of time. The combination of chrome, iron, and nickel in the #300 series stainless steel has a definite passive reaction with a titanylated sulfuric acid electrolyte.
Under the confined condition of a relatively close spacing and complete encapsulating seal of the cells, it has been found that the cell potential does not rise very much on overcharge, indicating that any hydrogen or oxygen that may have been generated is combined, thus preventing the polarization voltage characteristics common to standard lead/acid batteries.
Figs. 5 and 6 illustrate the adaptability of the cell elements to cylindrical forms, the structure shown having overall dimensions similar to a "D" size primary dry cell. Plastic con-tainer (24) houses positive and negative cylindrical electrodes, ~ - -(23) and (26) respectively, formed from the same materials utilized in the cell described in Fig. 1. The inner cylinder (23) -.

--`\
-having spot welded lead (22) is formed from expanded 0.060 thick titanium and the outer cylinder (2~) having spot welded tab ~27) is formed from 0.060 thick #304 stainless steel. The cylinders are nickel plated, then lead plated and thereafter coated and the spaces filled with lead oxide and processed in the same manner as the cell of Fig. 1. To increase the capacity, the cylinders may be corrugated before plating. After electro-forming, the cylinders are placed in the plastic container and the space between the two cylinders and the space inside the inner cylinder is filled with the gel titanylated sulfuric acid electrolyte (25). A form fitting polyethylene disc ~29) which serves the same purpose as the Saran (a trademark) wrapping in Fig. 1 and having two slots for the leads is forced into the container and rests upon the tops of the cylinders. Any space between the slots and the leads is filled with quick acting epoxy. The space between the sealing disc (29) and the top is also filled with epoxy resin ~30).

., .:. ., .~ .
', "', -

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electric storage battery having a positive electrode of lead peroxide supported by a grid of titanium with a first polarization inhibiting layer therebetween; a negative electrode of lead supported by a grid of stainless steel with a second polarization inhibiting layer therebetween, and an electrolyte of sulfuric acid, wherein the first and second polarization inhibiting layers are individually layers of cobalt or nickel.

2. A battery as claimed in Claim 1, in which the polarization inhibiting layers are layers of nickel.

3. The battery as claimed in Claim 1, in which electrolyte is gelled and substantially immobilized

4. A battery as claimed in Claim 1, wherein the sulfuric acid has dissolved therein a small amount of titanyl sulfate to inhibit dissolution of the titanium and of the stainless steel in said electrolyte.

5. The battery as claimed in Claim 4, in which the stainless steel grid is composed essentially of chromium, nickel and iron.

6. A battery as claimed in Claim 1, 2 or 3, in which a layer of lead is provided between the titanium and the lead peroxide and a dense plating of lead is provided between the stainless steel and the porous lead.

7. An electric storage battery having a positive electrode comprising a grid of titanium, a thin layer of nickel on the titanium, a dense layer of lead over the nickel and a coating of lead peroxide on said lead; a negative electrode comprising a grid of stainless steel, a thin layer of nickel on the stainless steel, a dense plating of lead on the nickel, a porous spongy coating of lead on said plated lead, and an electrolyte of sulfuric acid.

8. A hermetically sealed rechargeable cell comprising a container housing a positive electrode having a base of nickel plated titanium, a plating of lead over the nickel surface and a coating of lead peroxide over said lead; a negative electrode having a base of stainless steel of the type consisting preponderantly of iron and the balance substantially all chromium and nickel; a thick nickel plate over the stainless steel and a coating of porous spongy lead over said nickel surface; a spacer between said electrodes filled with an electrolyte of gelled sulfuric acid containing in the order of 1% titanyl sulfate dissolved therein, a resin impermeable and electrolyte inert plastic film tightly wrapped around said electrodes and spacer and sealing the same, said sealed cell being hermetically sealed by encapsulation in an epoxy resin serving to maintain the cell elements in pressure contact, said plastic film preventing contact of the epoxy resin with the electrolyte and reaction therewith.

9. An electric storage battery having a positive electrode comprising a grid of titanium, a first thin layer of one of the metals nickel and cobalt on said titanium; a second layer of dense plated lead over said first layer; and a coating of lead peroxide electro-formed from a lead oxide mixture bonded to said second layer; a negative electrode comprising a grid of stainless steel having a thin layer of one of the metals nickel and cobalt and a dense plating of lead thereover; a porous spongy coating of lead on said dense plated lead; and an electrolyte consisting preponderantly of sulfuric acid having a small amount of titanyl sulfate dissolved therein.